Lithographic mask and manufacturing method thereof

ABSTRACT

Cleaning is carried out by using a sulfuric acid type detergent at a resist stripping and cleaning step (step  5 ) in a semitranslucent portion forming process and a resist stripping and cleaning step (step  10 ) in a shielding band forming process, and a sulfuric acid removing step of partially or wholly removing a surface layer portion in a pattern into which a sulfate ion is adsorbed is then carried out to effectively remove the adsorbed sulfate ion.

This application is a divisional of application Ser. No. 11/165,536,filed Jun. 24, 2005, which claims foreign priority based on JapanesePatent application No. 2004-188157, filed Jun. 25, 2004, the contents ofwhich is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of manufacturing alithographic mask such as a photomask to be used for manufacturing asemiconductor device and the lithographic mask, and to a method ofmanufacturing a lithographic mask to be used in an exposing deviceutilizing such high power exposing means as to promote the formingreaction of an ammonium sulfate type foreign matter, for example, anexposed light constituted by a laser beam having a wavelength of 200 nmor less such as an ArF excimer laser beam, and the lithographic mask.

2. Description of the Related Art

In the formation of a transfer pattern in the manufacture of asemiconductor device, for example, an exposed light is irradiated on aresist through a photomask (reticle), for example. In such a case, therehas conventionally been used a photomask in which a shielding filmpattern is formed on a transparent substrate. For the material of ashielding film, generally, a chromium type material (a chromium simplesubstance, chromium containing nitrogen, oxygen and carbon, or alaminated film formed by these material films) is used. In recent years,furthermore, a phase shift mask has been used practically in order toenhance the resolution of the transfer pattern.

Phase shift masks of various types have been known (an alternative type,an auxiliary pattern type and a self-alignment type). For one of them,there has been known a halftone type phase shift mask which is suitablefor the high resolution pattern transfer of a hole and a dot. In thehalftone type phase shift mask, a semitranslucent film pattern having aphase shift amount of approximately 180 degrees is formed on atransparent substrate, and the semitranslucent film is formed as asingle layer or a multilayer.

For example, JP No. 2966369 disclosed a semitranslucent film patternwhich is constituted by a thin film formed by a substance containing, asa main component, a metal such as molybdenum, silicon and nitrogen. Thesemitranslucent film constituted by the materials is formed by a singlelayer and can control a predetermined phase shift amount andtransmittance, and furthermore, is excellent in an acid resistance and alight resistance.

As described above, there has been considerably developed the filmmaterial to be used in the photomask which contains nitrogen in the filmfor various reasons.

When a pattern transfer is to be carried out by using the photomask(reticle), a laser beam is irradiated on the photomask. For this reason,there is a problem in that the formation of some deposit is promoted bya laser irradiation and the deposit becomes a foreign matter to stickonto the photomask. It has been confirmed that one of the deposits isammonium sulfate.

For the photomask, generally, cleaning (including a resist strippingtreatment and a treatment for removing a pellicle adhesive) using aliquid detergent containing S (sulfur) such as sulfuric acid (which willbe hereinafter referred to as a sulfuric acid type detergent) is carriedout for the resist stripping, the cleaning and the removal of thepellicle adhesive. However, it has been found that a sulfuric acidcomponent derived from the sulfuric acid type detergent used at thecleaning step described above is adsorbed into a photomask surface andis removed with difficulty, and therefore, the sulfuric acid componentremains in the photomask after the cleaning. It has been confirmed thatthese residues are different from each other depending on a pellicle oran environment for use and chemically react to an ammonia component inthe air to form and deposit ammonium sulfate in the state of a crystal.Moreover, there was inspected a material containing nitrogen which isused for a thin film to be utilized in the photomask. As a result, ithas been found that more ammonium ions (NH₄ ⁺) are present on thesurface of a thin film containing nitrogen than a thin film which doesnot contain the nitrogen. Accordingly, it can also be supposed that thenitrogen component in the thin film to be used in the photomask mightcontribute to the deposition of the ammonium sulfate which can be aforeign matter defect.

With the microfabriation of an LSI pattern in recent years,particularly, the wavelength of an exposed light source (the wavelengthof an exposed light) has increasingly been reduced from an existing KrFexcimer laser (248 nm) to an ArF excimer laser (193 nm) and an F₂excimer laser (157 nm). In such a situation, for example, in the case inwhich an exposed light source having a short wavelength such as the ArFexcimer laser is used, a laser output becomes high. Therefore, there isa problem in that the formation of a deposit can be promoted more easilyand a foreign matter is generated more remarkably, resulting in a greatinfluence on quality.

In the case in which the deposition of the ammonium sulfate isrecognized on the surface of the photomask, a quality abnormality iscaused so that it is necessary to carry out cleaning or fabricationagain.

SUMMARY OF THE INVENTION

In consideration of the circumstances, it is an object of the inventionto provide a method of manufacturing a lithographic mask which cansuppress the amount of a sulfuric acid component remaining on thelithographic mask which causes the deposition of ammonium sulfate and/orcan suppress the generation of the ammonium component of thelithographic mask which causes the deposition of the ammonium sulfate,thereby controlling the deposition of the ammonium sulfate when exposinga light from such high power exposing means as to promote the formingreaction of a foreign matter constituted by the ammonium sulfate, forexample, an ArF excimer laser.

Furthermore, it is an object of the invention to provide a lithographicmask capable of suppressing the generation of the ammonia component ofthe lithographic mask which causes the deposition of ammonium sulfate,thereby controlling the deposition of the ammonium sulfate when exposinga light from such high power exposing means as to promote the formingreaction of a foreign matter constituted by the ammonium sulfate, forexample, an ArF excimer laser.

In order to solve the problems, first means is directed to a method ofmanufacturing a lithographic mask including a desirable pattern on asubstrate which is to be used in an exposing device utilizing such highpower exposing means as to promote a forming reaction of an ammoniumsulfate type foreign matter, comprising:

at least a step of forming the pattern, a cleaning step of carrying outcleaning using a sulfuric acid type detergent after the step of formingthe pattern, and a sulfuric acid removing step of partially or whollyremoving a surface layer portion of the pattern into which a sulfate ionis adsorbed after the cleaning step.

Second means is directed to the method of manufacturing a lithographicmask according to the first means, wherein the surface layer portioninto which the sulfate ion is adsorbed is a sulfate ion adsorbing layerprovided on a substrate or thin film for forming a pattern or thepattern before the cleaning step and before or after the step of formingthe pattern.

Third means is directed to a method of manufacturing a lithographic maskincluding a desirable pattern on a substrate which is to be used in anexposing device utilizing such high power exposing means as to promote aforming reaction of an ammonium sulfate type foreign matter, comprising:

at least a step of forming the pattern, a cleaning step of carrying outcleaning using a sulfuric acid type detergent after the step of formingthe pattern, and a sulfuric acid removing step using a non-sulfuric acidtype liquid at a temperature of 85° C. or more after the cleaning step.

Fourth means is directed to the method of manufacturing a lithographicmask according to any of the first to third means, wherein the patternhas a layer constituted by a material containing at least nitrogen on atleast an uppermost layer, the method further comprising a step ofcarrying out an ammonium ion formation preventing treatment for thelayer constituted by a material containing at least nitrogen before orafter forming the pattern.

Fifth means is directed to the method of manufacturing a lithographicmask according to the fourth means, wherein the ammonium ion formationpreventing treatment is obtained by combining at least one of a heattreatment, a light irradiation treatment and a surface oxidationtreatment.

Sixth means is directed to the method of manufacturing a lithographicmask according to the fourth or fifth means, wherein the cleaning stepis executed after the step of carrying out the ammonium ion formationpreventing treatment.

Seventh means is directed to a method of manufacturing a lithographicmask including a pattern having, on at least an uppermost layer, a layerconstituted by a material containing at least silicon and nitrogen on atransparent substrate which is to be used in an exposing deviceutilizing such high power exposing means as to promote a formingreaction of an ammonium sulfate type foreign matter, comprising at leastthe steps of:

forming the pattern of the layer constituted by the material containingat least silicon and nitrogen; and

carrying out an ammonium ion formation preventing treatment over thelayer constituted by the material containing at least silicon andnitrogen on which the pattern is formed.

Eighth means is directed to the method of manufacturing a lithographicmask according to the seventh means, wherein the ammonium ion formationpreventing treatment is obtained by combining at least one of a heattreatment, a light irradiation treatment and an oxidation treatment.

Ninth means is directed to the method of manufacturing a lithographicmask according to the seventh or eighth means, wherein the ammonium ionformation preventing treatment is carried out at a final step for thelithographic mask.

Tenth means is directed to the method of manufacturing a lithographicmask according to any of the first to ninth means, wherein thelithographic mask is a photomask to be used in an exposing device havingan exposed light in a wavelength of 200 nm or less.

Eleventh means is directed to the method of manufacturing a lithographicmask according to the tenth means, wherein the lithographic mask is aphase shift mask to be used in an exposing device including an ArFexcimer laser as an exposed light source, and the pattern has, on atleast an uppermost layer, a semitranslucent film containing molybdenum,silicon and nitrogen.

Twelfth means is directed to a lithographic mask to be a photomaskincluding a pattern having, on at least an uppermost layer, a layerconstituted by a material containing at least nitrogen on a transparentsubstrate which is to be used in an exposing device utilizing such highpower exposing means as to promote a forming reaction of a foreignmatter constituted by ammonium sulfate,

wherein the layer constituted by the material containing at leastnitrogen is subjected to surface reforming by an ammonium ion formationpreventing treatment carried out after forming the pattern.

Thirteenth means is directed to the lithographic mask according to thetwelfth means, wherein the lithographic mask is a photomask to be usedin an exposing device having an exposed light in a wavelength of 200 nmor less.

Fourteenth means is directed to the lithographic mask according to thethirteenth means, wherein the lithographic mask is a phase shift mask tobe used in an exposing device including an ArF excimer laser as anexposed light source, and the pattern has, on at least an uppermostlayer, a semitranslucent film containing molybdenum, silicon andnitrogen.

According to the method of manufacturing a lithographic mask inaccordance with the invention, it is possible to suppress the amount ofa sulfuric acid component remaining on the lithographic mask whichcauses the deposition of ammonium sulfate and/or to suppress thegeneration of the ammonia component of the lithographic mask whichcauses the deposition of the ammonium sulfate, thereby controlling thedeposition of the ammonium sulfate when exposing a light from such highpower exposing means as to promote the forming reaction of a foreignmatter constituted by the ammonium sulfate, for example, an ArF excimerlaser.

According to the lithographic mask in accordance with the invention,furthermore, it is possible to suppress the generation of the ammoniacomponent of the lithographic mask which causes the deposition ofammonium sulfate, thereby controlling the deposition of the ammoniumsulfate when exposing a light from such high power exposing means as topromote the forming reaction of a foreign matter constituted by theammonium sulfate, for example, an ArF excimer laser.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of the flow of a method ofmanufacturing a halftone type phase shift mask,

FIG. 2 is a view for explaining a sulfuric acid removing step accordingto an example 1,

FIG. 3 is a view for explaining a sulfuric acid removing step accordingto an example 2,

FIGS. 4A and 4B are views for explaining an ammonium ion formationpreventing treatment according to an example 4, and

FIGS. 5A and 5B are views for explaining an ammonium ion formationpreventing treatment according to an example 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described hereinbelow byreference to the drawings. Unless otherwise specifically defined in thespecification, terms have their ordinary meaning as would be understoodby those of ordinary skill in the art.

For example, in order to reduce the deposition of an ammonium sulfatetype foreign matter (including ammonium sulfate and an ammonia saltmainly containing the ammonium sulfate) when exposing a light from suchhigh power exposing means as to promote the forming reaction of theammonium sulfate type foreign matter, for example, an exposed lightconstituted by a laser beam having a wavelength of 200 nm or less suchas an ArF excimer laser beam, it is possible to propose a method ofreducing a sulfate ion on a lithographic mask and a method of reducingan ammonium ion.

First of all, a method of reducing a sulfate ion remaining in a sulfuricacid type detergent to be used at a cleaning step can be taken as themethod of reducing a sulfate ion.

A method of manufacturing a lithographic mask according to a firstembodiment of the invention is one of the methods of reducing a sulfateion remaining in a sulfuric acid type detergent to be used at thecleaning step, and has at least a sulfuric acid removing step ofpartially or wholly removing a surface layer portion in a pattern intowhich the sulfate ion is adsorbed after the cleaning step of carryingout cleaning by using the sulfuric acid type detergent.

More specifically, it is possible to reduce the residual sulfuric acidby partially or wholly removing the surface layer portions of thesurface and side wall of the pattern into which the sulfate ion isadsorbed.

At the sulfuric acid removing step, examples of the method of partiallyremoving the surface layer portion of the pattern include a method ofcarrying out slight etching by using a liquid in which the material ofthe surface layer portion can be dissolved and a method of sliding asubstance capable of physically removing the surface layer portion incontact such as a scrubbing method. In order to effectively remove theadsorbed sulfate ion, it is preferable that a depth for the removalshould be set to be equal to or greater than 10 Å.

For example, in case of a semitranslucent phase shift layer containingmolybdenum, silicon and nitrogen in a halftone type phase shift mask, itis possible to remove the surface layer portion by dipping into anon-sulfuric acid type liquid (a liquid containing no S (sulfur)) suchas pure water at 85° C. or more, the supply of the non-sulfuric acidtype liquid such as the supply of a puddle through a spin method or anexposure to a mist-like non-sulfuric acid type liquid. This treatment isexecuted as a rinse step after the cleaning, and furthermore, as aseparate step from the rinse step. The sulfuric acid removing step iscarried out as the rinse step after sulfuric acid cleaning, andfurthermore, the sulfuric acid removing step is carried out as anotherstep. Consequently, it is possible to shorten a time required for atreatment at the sulfuric acid removing step. At a separate step fromthe rinse, the treatment may be carried out successively after the rinseor after the execution of another cleaning treatment. The temperature ofthe liquid is preferably set to be equal to or higher than 85° C. inorder to effectively remove the sulfate ion and is more preferably setto be equal to or higher than 90° C. because the effect of removing thesulfate ion is rapidly enhanced.

Examples of the removal of the surface layer portion include dippinginto an alkaline solution or a fluoric acid solution, the supply of aliquid and an exposure to a mist-like liquid.

In order to carry out the sulfuric acid removing step and to prevent anoriginal pattern characteristic from being damaged, it is possible topropose a method of forming a pattern which anticipates a portion to beremoved.

In a method of manufacturing a lithographic mask according to a secondembodiment of the invention, the surface layer portion into which thesulfate ion is adsorbed is set to be a sulfate ion adsorbing layerformed on a substrate or thin film for forming a pattern or on thepattern before the cleaning step and before or after the step of formingthe pattern, and there will be disclosed another example of the methodof carrying out a sulfuric acid removing step and preventing an originalpattern characteristic from being damaged in the method of manufacturinga lithographic mask according to the first embodiment.

Examples of the method include a method of providing a new layer as asulfate ion adsorbing layer in a blank state before the formation of apattern before a cleaning step or after the formation of a patternbefore the cleaning step and a method in which an upper layer serves asthe sulfate ion adsorbing layer in a film having a multilayer structureand the cleaning step is carried out in a state in which the upper layeris present and the upper layer is then removed.

Furthermore, the sulfate ion adsorbing layer in this method includes alayer formed by carrying out surface finishing over the surface layerportion in the method of manufacturing a lithographic mask according tothe first embodiment, and the sulfuric acid removing step includes thepartial or whole removal of the surface finishing layer in the directionof a depth or the removal of the surface finishing layer and a lowerportion. Examples of the surface finishing include a treatment foroxidizing a surface layer portion (a heat treatment, a light irradiationand ashing). By changing a composition through the surface finishing, itis also possible to control an etching speed in the removal of thesurface layer portion, thereby controlling the amount of the removal.

In a method of manufacturing a lithographic mask according to a thirdembodiment of the invention, a method having at least a sulfuric acidremoving step using a non-sulfuric acid type liquid at a temperature of85° C. or more after a cleaning step of carrying out cleaning using asulfuric acid type detergent is employed as another method of reducing asulfate ion remaining in the sulfuric acid type detergent to be used atthe cleaning step.

According to this method, it is possible to effectively remove theresidual sulfate ion adsorbed into the lithographic mask.

This treatment may be carried out as both the rinse step after thecleaning and a separate step from the rinse step. By executing thesulfuric acid removing step as the rinse step after the sulfuric acidcleaning, and furthermore, the sulfuric acid removing step as anotherstep, it is possible to shorten a time required for processing thesulfuric acid removing step. In the case in which the treatment is to becarried out as the separate step from the rinse, it may be executedsuccessively after the rinse or after the execution of another cleaning.Moreover, the sulfuric acid removing step according to the embodimentalso includes the case in which the surface layer portion of a patternis not removed. It is preferable that the temperature of a liquid shouldbe set to be equal to or higher than 90° C. because the effect ofremoving a sulfate ion is rapidly enhanced.

Moreover, the sulfuric acid removing step can be carried out by dippinginto a non-sulfuric acid type liquid, the supply of the non-sulfuricacid type liquid such as the supply of a puddle through a spin method,or an exposure to a mist-like non-sulfuric acid type liquid.

Next, a method of manufacturing a lithographic mask according to afourth embodiment serves to reduce the presence of an ammonium ion inaddition to the sulfuric acid removing step, and has a step of carryingout an ammonium ion formation preventing treatment over the layerconstituted by a material containing at least nitrogen before or afterthe formation of a pattern.

As the method of reducing an ammonium ion, it is possible to propose amethod of suppressing the generation of the ammonium ion from a thinfilm containing nitrogen. According to the embodiment, however, it ispossible to suppress the ammonium ion generated from the thin filmcontaining nitrogen.

Referring to the ammonium ion formation preventing treatment, theconcentration of an ammonium ion (NH₄ ⁺) is more decreased than thatbefore the treatment when the concentration of the NH₄ ⁺ is measured byion chromatography through a pure water extraction over a surfacesubjected to the treatment. This treatment is carried out in such amanner that the concentration of the NH₄ ⁺ measured by the ionchromatography is equal to or lower than 20 ng/cm², is preferably equalto or lower than 10 ng/cm², and is further preferably equal to or lowerthan 5 ng/cm², for example.

The ammonium ion formation preventing treatment may be carried out in ablank state before the formation of a pattern or after the formation ofthe pattern (after an etching step). By executing the treatment afterthe formation of the pattern, it is possible to carry out surfacefinishing over the side wall of the pattern, which is preferable.

Examples of the thin film containing nitrogen in a lithographic maskinclude a shielding film in a photomask, a reflection preventing filmand a semitranslucent film in a halftone type phase shift mask. Thesemitranslucent film in the halftone type phase shift mask has a singlelayer structure and a multilayer structure, and examples of the materialof the semitranslucent film having the single layer structure include amaterial containing silicon and nitrogen, a material containing a metal,silicon and nitrogen, or a material containing at least one selectedfrom oxygen, fluorine, carbon and hydrogen therein. The metal containsat least one selected from molybdenum, tantalum, tungsten, chromium,titanium, nickel, palladium, hafnium and zirconium, and thesemitranslucent film having the multilayer structure includes a filmformed by at least two material films of the semitranslucent film havingthe single layer structure, a transmittance regulating layer such as ametal film containing at least one selected from chromium, tantalum,hafnium, magnesium, aluminum, titanium, vanadium, yttrium, zirconium,niobium, molybdenum, tin, lanthanum, tungsten and silicon, and a filmformed by laminating the material of the single layer (a halftone film).The semitranslucent film has a phase difference set to be approximately180 degrees and a transmittance selected from a range of 3 to 40% inorder to obtain a phase shift effect.

Since it can be supposed that the ammonium ion formation preventingtreatment has a treating efficiency reduced by the influence of thesulfate ion adsorbed at the cleaning step, it is preferable that thesame treatment should be carried out before the cleaning step using thesulfuric acid type detergent or after the sulfuric acid removing step ifit is to be executed after the cleaning step. In some cases, moreover, acleaning resistance or warm water resistance of a pattern is enhanced asa result of the stabilization of the surface layer portion by theammonium ion formation preventing treatment. In a pattern formed by amaterial containing molybdenum, silicon and nitrogen to be used in ahalftone type phase shift mask, for example, in some cases in which thesulfuric acid removing step using the warm water (for example, 85° C. ormore) is carried out, the warm water resistance is insufficient so thatan optical characteristic is changed. Thus, there is a possibility thatthe characteristic of the pattern might be changed at the sulfuric acidremoving step. In the case in which the change in the characteristic canbe reduced by the ammonium ion formation preventing treatment, it ispreferable that the ammonium ion formation preventing treatment shouldbe carried out before the sulfuric acid removing step. Furthermore, theammonium ion formation preventing treatment may be carried out pluraltimes.

In a method of manufacturing a lithographic mask according to a fifthembodiment, the ammonium ion formation preventing treatment is combinedwith at least one of a heat treatment, a light irradiation treatment anda surface oxidation treatment.

Examples of the heat treatment include a surface thermal oxidationtreatment in the air or an oxygen or carbon dioxide atmospherecontaining the oxygen, or a heat treatment in an inert gas atmospheresuch as nitrogen or argon or in vacuum. It can be supposed that theformation of an ammonium ion is suppressed by the promotion andstabilization of the rearrangement of a film structure through the heattreatment. A heat treatment temperature is equal to or higher than 180°C. and is preferably equal to or higher than 250° C. Moreover, a timerequired for the heat treatment is varied depending on the treatmenttemperature and the treatment atmosphere, and is equal to or longer than5 minutes at a minimum and is preferably equal to or longer than 10minutes in consideration of the uniform application of a heat. In somecases in which the heat treatment temperature exceeds 400° C., areaction to the surface of a thin film sensitively progresses in anactive atmosphere containing oxygen, for example, and there is apossibility that the function of the thin film might be damaged. Forthis reason, it is preferable that the heat treatment should be carriedout in an atmosphere in which oxygen is not contained or theconcentration of the oxygen is sufficiently controlled.

A light irradiation can be executed by using a light having a wavelengthof 200 nm or less, for example, an excimer UV irradiating device havinga wavelength of 172 nm which is used as an irradiating light source incleaning. The light irradiation can be treated in the air or in anoxygen or carbon dioxide atmosphere containing the oxygen. Anirradiating output is equal to or higher than 10 mW and is preferablyequal to or higher than 30 mW, and a time required for an irradiation isequal to or longer than 5 minutes and is preferably equal to or longerthan 10 minutes.

Examples of the surface oxidation treatment include ashing, ionimplantation and ozone oxidation in the oxygen atmosphere in addition tothe thermal oxidation treatment and the photooxidation treatment. Byincreasing the content of the oxygen on the surface through the surfaceoxidation treatment, it is possible to suppress the formation of anammonium ion.

In a method of manufacturing a lithographic mask according to a sixthembodiment, the cleaning step in the method according to the fourth orfifth embodiment is carried out after the step of executing the ammoniumion formation preventing treatment.

According to this method, the ammonium ion formation preventingtreatment is carried out before a contact with a liquid such as asulfuric acid type cleaning solution to be used at the cleaning step.Therefore, the ammonium ion formation preventing treatment has a hightreating efficiency. Furthermore, there is a possibility that thecharacteristic of a pattern might be changed at the cleaning step or asulfuric acid removing step. In the case in which the change in thecharacteristic can be reduced by the ammonium ion formation preventingtreatment, the cleaning step is carried out after the ammonium ionformation preventing treatment so that the change in the characteristicof the pattern can be suppressed.

A method of manufacturing a lithographic mask according to a seventhembodiment serves to reduce the presence of an ammonium ion and tomanufacture a lithographic mask including a pattern having, on at leastan uppermost layer, a layer constituted by a material containing atleast silicon and nitrogen on a transparent substrate which is to beused in an exposing device utilizing such high power exposing means asto promote a forming reaction of a foreign matter constituted byammonium sulfate, comprising at least the steps of forming the patternof the layer constituted by the material containing at least silicon andnitrogen, and carrying out an ammonium ion formation preventingtreatment over the layer constituted by the material containing at leastsilicon and nitrogen on which the pattern is formed.

As the method of reducing an ammonium ion, it is possible to propose amethod of suppressing the ammonium ion generated from a thin filmcontaining nitrogen. According to the method of manufacturing alithographic mask in accordance with the seventh embodiment, however, itis possible to suppress the ammonium ion generated from the thin filmcontaining nitrogen.

Referring to the ammonium ion formation preventing treatment, theconcentration of an ammonium ion (NH₄ ⁺) is more decreased than thatbefore the treatment when the concentration of the NH₄ ⁺ is measured byion chromatography through a pure water extraction over a surfacesubjected to the treatment. This treatment is carried out in such amanner that the concentration of the NH₄ ⁺ measured by the ionchromatography is equal to or lower than 20 ng/cm², is preferably equalto or lower than 10 ng/cm², and is further preferably equal to or lowerthan 5 ng/cm², for example.

By carrying out the ammonium ion formation preventing treatment afterthe formation of a pattern (after an etching step), it is possible toexecute surface finishing over the side wall of the pattern.

Examples of the thin film containing nitrogen in a lithographic maskinclude a shielding film in a photomask, a reflection preventing filmand a semitranslucent film in a phase shift mask. The semitranslucentfilm in a halftone type phase shift mask has a single layer structureand a multilayer structure, and examples of the material of thesemitranslucent film having the single layer structure include amaterial containing silicon and nitrogen, a material containing a metal,silicon and nitrogen, or a material containing at least one selectedfrom oxygen, fluorine, carbon and hydrogen therein. The metal containsat least one selected from molybdenum, tantalum, tungsten, chromium,titanium, nickel, palladium, hafnium and zirconium, and thesemitranslucent film having the multilayer structure includes a filmformed by laminating at least two material films of the semitranslucentfilm having the single layer structure, a transmittance regulating layersuch as a metal film containing at least one selected from chromium,tantalum, hafnium, magnesium, aluminum, titanium, vanadium, yttrium,zirconium, niobium, molybdenum, tin, lanthanum, tungsten and silicon,and a film formed by laminating the material of the single layer (ahalftone film). The semitranslucent film of the halftone type phaseshift mask has a phase difference set to be approximately 180 degreesand a transmittance selected from a range of 3 to 40% in order to obtaina phase shift effect. Furthermore, examples of a phase shift mask otherthan the halftone type phase shift mask includes a phase shift mask inwhich a semitranslucent film does not substantially have a phase shiftfunction but said function is caused by trimming a substrate. In thiscase, it is possible to propose a semitranslucent film which has thematerial of the single layer halftone type phase shift mask on at leastan upper layer.

In the method of manufacturing a lithographic mask according to theseventh embodiment, moreover, in the case in which the cleaning usingthe sulfuric acid type cleaning solution is to be carried out, aprocessing of suppressing a residual sulfuric acid ion as much aspossible is executed or only cleaning using a non-sulfuric acid typecleaning solution is performed to reduce the presence of a sulfate ionwhich is another cause of deposition of the ammonium sulfate.Consequently, it is possible to prevent the deposition of an ammoniumsulfate type foreign matter more effectively.

In the ammonium ion formation preventing treatment, it can be supposedthat a treating efficiency is reduced by the influence of the sulfateion to be adsorbed at the cleaning step when the cleaning is to becarried out by using the sulfuric acid type detergent. Therefore, it ispreferable that the treatment should be carried out before the cleaningstep using the sulfuric acid type detergent or after the sulfuric acidremoving step if it is to be executed after the cleaning step. In thecase in which there is a possibility that the characteristic of thepattern might be changed at the cleaning step and the change in thecharacteristic can be reduced by the ammonium ion formation preventingtreatment, moreover, it is preferable that the ammonium ion formationpreventing treatment should be carried out before the same step.Furthermore, the ammonium ion formation preventing treatment may becarried out plural times.

In a method of manufacturing a lithographic mask according to an eighthembodiment, the ammonium ion formation preventing treatment in themethod of manufacturing a lithographic mask according to the seventhembodiment is combined with at least one of a heat treatment, a lightirradiation treatment and a surface oxidation treatment.

Examples of the heat treatment include a surface thermal oxidationtreatment in the air or an oxygen or carbon dioxide atmospherecontaining the oxygen, or a heat treatment in an inert gas atmospheresuch as nitrogen or argon or in vacuum. It can be supposed that theformation of an ammonium ion is suppressed by the promotion andstabilization of the rearrangement of a film structure through the heattreatment. A heat treatment temperature is equal to or higher than 180°C. and is preferably equal to or higher than 250° C. Moreover, a timerequired for the heat treatment is varied depending on the treatmenttemperature and the treatment atmosphere, and is equal to or longer than5 minutes at a minimum and is preferably equal to or longer than 10minutes in consideration of the uniform application of a heat. In somecases in which the heat treatment temperature exceeds 400° C., areaction to the surface of a thin film sensitively progresses in anactive atmosphere containing oxygen, for example, and there is apossibility that the function of the thin film might be damaged. Forthis reason, it is preferable that the heat treatment should be carriedout in an atmosphere in which oxygen is not contained or theconcentration of the oxygen is sufficiently controlled.

A light irradiation can be executed by using a light having a wavelengthof 200 nm or less, for example, an excimer UV irradiating device havinga wavelength of 172 nm which is used as an irradiating light source incleaning. The light irradiation can be treated in the air or in anoxygen or carbon dioxide atmosphere containing the oxygen. Anirradiating output is equal to or higher than 10 mW and is preferablyequal to or higher than 30 mW, and a time required for an irradiation isequal to or longer than 5 minutes and is preferably equal to or longerthan 10 minutes.

Examples of the surface oxidation treatment include ashing, ionimplantation and ozone oxidation in the oxygen atmosphere in addition tothe thermal oxidation treatment and the photooxidation treatment. Byincreasing the content of the oxygen on the surface through the surfaceoxidation treatment, it is possible to suppress the formation of anammonium ion.

In a method of manufacturing a lithographic mask according to a ninthembodiment, the ammonium ion formation preventing treatment in themethod of manufacturing a lithographic mask according to the seventh oreighth embodiment is carried out at the final step of the lithographicmask. More specifically, the resistance of the ammonia formationpreventing treatment is exceeded through cleaning using the sulfuricacid type detergent, a rinse using warm pure water and other treatingsteps after the execution of the ammonia formation preventing treatmentin some cases. In consideration of that respect, in case of a photomask,for example, the ammonia formation preventing treatment is carried outat a final step before the attachment of a pellicle. In the use of themask, consequently, it is possible to prevent the deposition of theammonium sulfate type foreign matter in use for an exposing deviceutilizing such high power exposing means as to promote the formingreaction of the ammonium sulfate type foreign matter. The ammoniaformation preventing treatment to be carried out herein may be areprocessing for supplementing the effect of the ammonium ion formationpreventing treatment executed in a process for manufacturing the mask.

In a method of manufacturing a lithographic mask according to a tenthembodiment, the method of manufacturing a lithographic mask according toeach of the first to ninth embodiments is suitably used in order tomanufacture a photomask to be used in an exposing device having anexposed light in a wavelength of 200 nm or less which includes an ArFexcimer laser (193 nm) and an F₂ excimer laser (157 nm), for example.Consequently, it is possible to suppress the formation of a foreignmatter constituted by ammonium sulfate which becomes a problem when theexposed light having a wavelength of 200 nm or less is irradiated.

In a method of manufacturing a lithographic mask according to aneleventh embodiment, the lithographic mask is a phase shift mask to beused in an exposing device comprising an ArF excimer laser as anexposing light source. Referring to the pattern, it is possible tosuitably use the method of manufacturing a lithographic mask accordingto the tenth embodiment in order to manufacture a phase shift maskhaving a semitranslucent film containing molybdenum, silicon andnitrogen on at least an uppermost layer.

Examples of such a phase shift mask include a single layer halftone typephase shift mask comprising a semitranslucent layer to be a singlelayer, a multilayer halftone type phase shift mask comprising asemitranslucent layer having a multilayer phase shift function includinga layer containing molybdenum, silicon and nitrogen on an upper layer,and a phase shift mask in which the semitranslucent layer does notsubstantially have the phase shift function and is caused to have thephase shift function by trimming a substrate.

A lithographic mask according to a twelfth embodiment can reduce thepresence of an ammonium ion and a lithographic mask according to athirteenth embodiment is a photomask including a pattern having, on atleast an uppermost layer, a layer constituted by a material containingat least nitrogen on a transparent substrate which is to be used in anexposing device utilizing such high power exposing means as to promote aforming reaction of a foreign matter constituted by ammonium sulfate,and the layer constituted by the material containing at least nitrogenis subjected to surface reforming by an ammonium ion formationpreventing treatment carried out after forming the pattern.

Referring to the ammonium ion formation preventing treatment, theconcentration of an ammonium ion (NH₄ ⁺) is more decreased than thatbefore the treatment when the concentration of the NH₄ ⁺ is measured byion chromatography through a pure water extraction over a surfacesubjected to the treatment. This treatment is carried out in such amanner that the concentration of the NH₄ ⁺ measured by the ionchromatography is equal to or lower than 20 ng/cm², is preferably equalto or lower than 10 ng/cm², and is further preferably equal to or lowerthan 5 ng/cm², for example.

More specifically, the surface reforming gives a surface layer in whicha composition is changed or the quality of a film is deterioratedthrough at least one of a heat treatment, a light irradiation treatmentand a surface oxidation treatment. It is preferable that a depth shouldbe equal to or greater than 10 Å in order to obtain an ammonium ionformation preventing effect.

Examples of the thin film containing nitrogen in a lithographic maskinclude a shielding film in a photomask, a reflection preventing filmand a semitranslucent film in a phase shift mask. The semitranslucentfilm in a halftone type phase shift mask has a single layer structureand a multilayer structure, and examples of the material of thesemitranslucent film having the single layer structure include amaterial containing silicon and nitrogen, a material containing a metal,silicon and nitrogen, or a material containing at least one selectedfrom oxygen, fluorine, carbon and hydrogen therein, for example. Themetal contains at least one selected from molybdenum, tantalum,tungsten, chromium, titanium, nickel, palladium, hafnium and zirconium,and the semitranslucent film having the multilayer structure includes afilm formed by laminating at least two material films of thesemitranslucent film having the single layer structure, a transmittanceregulating layer such as a metal film containing at least one selectedfrom chromium, tantalum, hafnium, magnesium, aluminum, titanium,vanadium, yttrium, zirconium, niobium, molybdenum, tin, lanthanum,tungsten and silicon, and a film formed by laminating the material ofthe single layer (a halftone film). The semitranslucent film in thehalftone type phase shift mask has a phase difference set to beapproximately 180 degrees and a transmittance selected from a range of 3to 40% in order to obtain a phase shift effect. Furthermore, examples ofa phase shift mask other than the halftone type phase shift mask includea phase shift mask in which a semitranslucent film does notsubstantially have a phase shift function and is caused to have thephase shift function by trimming a substrate. In this case, it ispossible to propose a semitranslucent film which has the material of thesingle layer halftone type phase shift mask on at least an upper layer.

According to a lithographic mask in accordance with the thirteenthembodiment, the lithographic mask according to the twelfth embodiment issuitably used as a photomask to be utilized in an exposing device havingan exposed light in a wavelength of 200 nm or less which includes an ArFexcimer laser (193 nm) and an F₂ excimer laser (157 nm), for example.Consequently, it is possible to suppress the formation of a foreignmatter constituted by ammonium sulfate which becomes a problem when theexposed light having a wavelength of 200 nm or less is irradiated.

A lithographic mask according to a fourteenth embodiment is obtained bysetting the lithographic mask according to the thirteenth embodiment tobe a phase shift mask to be used in an exposing device comprising an ArFexcimer laser as an exposed light source, and the pattern is set to havea semitranslucent film containing molybdenum, silicon and nitrogen on atleast an uppermost layer. In order to manufacture the phase shift maskin the lithographic mask according to the embodiment, it is possible tosuitably use the lithographic mask according to the thirteenthembodiment.

Examples of such a phase shift mask include a single layer halftone typephase shift mask comprising a semitranslucent layer to be a singlelayer, a multilayer halftone type phase shift mask comprising asemitranslucent layer having a multilayer phase shift function includinga layer containing molybdenum, silicon and nitrogen on an upper layer,and a phase shift mask in which the semitranslucent layer does notsubstantially have the phase shift function and is caused to have thephase shift function by trimming a substrate.

The invention will be described below in more detail with reference toexamples applied to the method of manufacturing a halftone type phaseshift mask.

EXAMPLE 1

FIG. 1 shows an example of the flow of a method of manufacturing ahalftone type phase shift mask to be a kind of a photomask.

First of all, there is prepared a photomask blank 1 in which asemitranslucent film 3 having a single layer structure constitutedsubstantially by a metal such as molybdenum, silicon and nitrogen isformed on a transparent substrate 2, a chromium type shielding film 4 isformed thereon, and furthermore, a resist film 5 is formed thereon (FIG.1 (step 1)). The semitranslucent film 3 is formed on the transparentsubstrate 2 by reactive sputtering (DC sputtering) in a mixed gasatmosphere of argon (Ar) and nitrogen (N₂) (Ar:N₂=10%:90%, pressure 0.2Pa) using a mixing target (Mo:Si=8:92 mol %) of molybdenum (Mo) andsilicon (Si). The photomask blank 1 is used for an ArF excimer laser (awavelength of 193 nm) having a transmittance of 5.5% and a phase shiftamount of approximately 180 degrees.

Next, the resist film 5 is subjected to writing (FIG. 1 (step 2)), and aprocess treatment such as development and baking (FIG. 1 (step 3)) inorder to form a pattern. Thus, a resist pattern 5 a is formed. Next, theshielding film 4 is etched to form a shielding portion 4 a through dryetching (FIG. 1 (step 4)) using a CF₄+O₂ gas, and subsequently, thesemitranslucent film 3 is subjected to etching to form a semitranslucentportion 3 a by using the resist pattern 5 a and the shielding portion 4a as a mask and resist stripping and cleaning are carried out (FIG. 1(step 5)) so that a semitranslucent portion is fabricated (the steps 1to 5 will be referred to as a semitranslucent portion forming process).

Then, a resist film 6 is coated over the substrate in which thesemitranslucent portion fabricating process has been completed (FIG. 1(step 6)). Thereafter, the resist film 6 in a region in which theshielding portion 4 a is unnecessary (the transfer region of a mask) isdrawn (FIG. 1 (step 7)), and a process treatment such as development andbaking (FIG. 1 (step 8)) is carried out to form a resist film pattern 6a so that the unnecessary portion of the shielding portion 4 a isexposed. Furthermore, the shielding portion 4 a exposed by the etchingis subjected to the etching (FIG. 1 (step 9)), and resist stripping andcleaning (FIG. 1 (step 10)) are carried out to form a shielding band 4 bin the peripheral portion of the transfer region of the mask (the steps6 to 10 will be referred to as a shielding band forming process).

Thereafter, a CD measurement, a defect inspection and a correction of apattern defect (FIG. 1 (step 11)) are carried out. In the case in whichthe quality of the photomask can be guaranteed by final cleaning (FIG. 1(step 12)) and an inspection (FIG. 1 (step 13)), the attachment of apellicle (FIG. 1 (step 14)) is executed.

In the example 1, a sulfuric acid removing step is executed. FIG. 2 is aview for explaining the sulfuric acid removing step according to theexample 1.

In the example, a mixed solution 7 of sulfuric acid and perwater at 100°C. was used in the resist stripping carried out at the step 5 to be theresist stripping and cleaning step in the semitranslucent portionforming process and the step 10 to be the resist stripping and cleaningstep in the shielding band forming process, and a warm pure water 8 at92° C. was used in a subsequent rinse in the process described withreference to FIG. 1. The rinse step corresponds to the sulfuric acidremoving step according to the invention. At the rinse step, a purewater heating device 9 for a semiconductor which has been put on themarket has a limit of approximately 85° C. in respect of the safety ofthe device and a guarantee for performance. For this reason, warm purewater at 75° C. supplied from the pure water heating device was fed to adipping vessel 10 formed of quartz and a heater 11 for raising atemperature was provided on the outside of the dipping vessel to raisethe temperature of the pure water to 92° C.

After the step 10 was executed, the concentration of a sulfate ion onthe surface of the mask was measured by ion chromatography. As a result,the concentration of the sulfate ion was 0.2 ng/cm² and a reduction inthe concentration of the sulfate ion was found.

According to the example, therefore, it is possible to reduce asubstance to be the origin of the depositing reaction of an ammoniumsulfate type foreign matter through the irradiation of an exposed lightby executing the sulfuric acid removing step. As a result, it ispossible to reduce the deposition of the ammonium sulfate type foreignmatter.

While the sulfuric acid removing step has been carried out at both ofthe steps 5 and 10 in the example, a part of the shielding portion 4 ainto which the sulfate ion is adsorbed at the step 5 is removed by theetching at the step 9. For this reason, the sulfuric acid removing stepof the sulfate ion adsorbed at the step 5 may serve as the etching ofthe shielding portion 4 a at the step 9 in place of the step 5.

COMPARATIVE EXAMPLE 1

For a comparison, the same treatment as that in the example was carriedout except that a pure water rinse temperature in the example 1 was setto be 75° C. At that time, the concentration of the sulfate ion on thesurface of the mask was 1.7 ng/cm² in a measuring method on the samecondition as that in the example 1.

EXAMPLE 2

An example 2 is another example of the execution of the sulfuric acidremoving step and FIG. 3 is a view for explaining the sulfuric acidremoving step according to the example 2.

In the example, at the rinse step using warm pure water at 92° C. in theexample 1, a spin treatment is executed while discharging a warm purewater mist 12 at 75° C. and a dipping treatment at 92° C. is used as anext rinse step.

According to the example, the supply of the warm pure water of the purewater heating device 9 is limited by only the same dipping treatment asthat in the example 1. For this reason, a liquid substitution efficiencyin the warm pure water dipping vessel 10 is deteriorated and thesulfuric acid removing step (a time required for the treatment of thewarm pure water) is prolonged. According to circumstances, a warm waterresistance is not sufficient. Consequently, the optical characteristicof a semitranslucent film is changed. By setting a spinning methodhaving a high substitution efficiency as a prerinse step to removeresidual sulfuric acid in a short time, therefore, it is possible toshorten a time required for a dipping treatment at 92° C. to be a nextrinse step. As a result, it is possible to suppress a fluctuation in theoptical characteristic of a semitranslucent film. While the warm purewater at 75° C. has been used at the prerinse step, the actualtemperature of the warm pure water is lower than 75° C. by the emissionof a heat caused by the emission of air in the discharge and the heatabsorbing action of a substrate.

As a result of the execution of the rinse step, the concentration of asulfate ion was equal to that in the example 1.

According to the example, therefore, it is possible to reduce thedeposition of an ammonium sulfate type foreign matter in the same manneras in the example 1.

EXAMPLE 3

An example 3 is a further example of the execution of the sulfuric acidremoving step and FIG. 3 is a view for explaining the example 1. In theexample, a mixed solution of sulfuric acid and perwater at 100° C. wasused in resist stripping at the steps 5 and 10 and a normal lowtemperature rinse (a room temperature to 40° C.) was carried out, andwarm pure water at 92° C. was used in cleaning before the attachment ofa pellicle at the step 12.

As a result, the concentration of the sulfate ion after the cleaning wasequal to that in the example 1.

According to the example, therefore, it is possible to reduce thedeposition of an ammonium sulfate type foreign matter in the same manneras in the example 1.

EXAMPLE 4

An example 4 is an example of the execution of an ammonium ion formationpreventing treatment and FIGS. 4A and 4B are the views for explainingthe ammonium ion formation preventing treatment according to the example4.

In the example, the semitranslucent film exposed at the step 9 in theprocess described with reference to FIG. 1 was subjected to a heattreatment at approximately 350° C. for approximately 20 minutes in anair atmosphere (FIG. 4A). An arrow in FIGS. 4A and 4B typically indicatea state in which the heat treatment is carried out.

Referring to a surface condition before and after this treatment, ananalysis was carried out by an X-ray photoelectron spectral analyzingmethod. As a result, an O (oxygen) concentration was increased to be 55atomic I, an N (nitrogen) concentration was decreased to 30 atomic %,and a depth in which a change in a composition was recognized wasapproximately 15 Å.

Next, a resist was stripped at the step 10 and the concentration ofammonium on the surface of a semitranslucent film was then measured byion chromatography. As a result, the concentration was 108 ng/cm² in asample having no ammonium formation preventing treatment and was 1.3ng/cm² in a sample having the ammonium formation preventing treatment.

While the ammonium formation preventing treatment was carried out in astate in which the resist at the step 9 remains in the example 4, thesame advantages were obtained by the execution of the treatment over asemitranslucent film exposed by resist stripping and cleaning at thestep 10 (FIG. 4B).

According to the example, it is possible to reduce a substance to be theorigin of the depositing reaction of an ammonium sulfate type foreignmatter by the irradiation of an exposed light through the execution ofthe ammonium ion formation preventing treatment. As a result, it ispossible to reduce the deposition of the ammonium sulfate type foreignmatter.

EXAMPLE 5

An example 5 is another example of the execution of the ammonium ionformation preventing treatment and FIGS. 5A and 5B are the views forexplaining the ammonium ion formation preventing treatment according tothe example 5.

In the example 5, a continuous irradiation was executed in the air forapproximately 15 minutes by using an excimer UV irradiating devicehaving a wavelength of λ=172 nm in place of the heat treatment in theexample 4 (FIG. 5A). An arrow in FIGS. 4A and 4B typically indicate astate in which a UV irradiation is carried out. A resist was strippedand the concentration of ammonium on the surface of a semitranslucentfilm was then measured by ion chromatography. As a result, theconcentration was 108 ng/cm² in a sample having no ammonium formationpreventing treatment and was 3.7 ng/cm² in a sample having the ammoniumformation preventing treatment. From the result, it can be supposed thata surface reforming layer is formed by this treatment in the same manneras in the example 4.

While the ammonium formation preventing treatment has been carried outin a state in which the resist at the step 9 remains in the example 5,the same advantages were obtained by the execution of the treatment overthe semitranslucent film exposed by resist stripping and cleaning at thestep 10 (FIG. 5B).

According to the example, therefore, it is possible to reduce thedeposition of an ammonium sulfate type foreign matter in the same manneras in the example 4.

EXAMPLE 6

An example 6 is an example in which both the sulfuric acid removing stepand the ammonium ion formation preventing treatment are executed.

In the example, the ammonium ion formation preventing treatment wascarried out by the execution of the same heat treatment as that in theexample 4 at the step 9. Then, the sulfuric acid removing step wascarried out by using the same mixed solution 7 of sulfuric acid andperwater at 100° C. as that in the example 1 in the resist stripping atthe step 10, and the warm pure water 8 at 92° C. in a subsequent rinse.

According to the example, an ammonium ion can be decreased equivalentlyto the example 4 by the ammonium ion formation preventing treatment, andfurthermore, a cleaning solution resistance and a warm water resistancein a semitranslucent film are increased. Therefore, it is possible toreduce a decrease in the semitranslucent film by the treatment at thestep 10, thereby preventing a change in an optical characteristic.

At the sulfuric acid removing step to be carried out at the step 10,furthermore, it is also possible to reduce a sulfate ion in the samemanner as in the example 1.

According to the example, it is possible to reduce both of substances tobe the origin of the depositing reaction of an ammonium sulfate typeforeign matter through the irradiation of an exposed light by executingboth the sulfuric acid removing step and the ammonium ion formationpreventing treatment. As a result, it is possible to reduce thedeposition of the ammonium sulfate type foreign matter.

EXAMPLE 7

An example 7 is another example in which both the sulfuric acid removingstep and the ammonium ion formation preventing treatment are executed.

In the example, there was executed a sulfuric acid removing step ofremoving the ammonium ion formation preventing layer provided at thestep 9 in the example 6 through the cleaning before the attachment of apellicle at the step 12. In the example, the sulfuric acid removing stepwas carried out to partially remove the ammonium ion formationpreventing layer by using warm pure water at 92° C. and a strongalkaline liquid. As a result, it is possible to remove a sulfate ion ina surface layer portion, and furthermore, to suppress the generation ofan ammonium ion from a semitranslucent film.

According to the example, it is possible to reduce both of substances tobe the origin of the depositing reaction of an ammonium sulfate typeforeign matter through the irradiation of an exposed light by executingboth the sulfuric acid removing step and the ammonium ion formationpreventing treatment. As a result, it is possible to reduce thedeposition of the ammonium sulfate type foreign matter.

In the example, the ammonium ion formation preventing layer is reducedby the removal. In order to supplement an ammonium ion formationpreventing effect, therefore, an ammonium ion formation preventingprocess may be carried out again before the attachment of a pellicle byusing the same method as that in the example 4, for instance.

The invention is not restricted to the examples described above.

While the description has been given to the halftone type phase shiftmask for the ArF excimer laser in the examples, the invention can beapplied to a lithographic mask to be used in an exposing deviceutilizing such high power exposing means as to promote the formingreaction of an ammonium sulfate type foreign matter, for example, aphotomask such as another phase shift mask and a radiation mask such asan X ray, EUV or an electron beam.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the described preferredembodiments of the present invention without departing from the spiritor scope of the invention. Thus, it is intended that the presentinvention cover all modifications and variations of this inventionconsistent with the scope of the appended claims and their equivalents.

1.-18. (canceled)
 19. A lithographic mask to be a photomask including apattern having, on at least an uppermost layer, a layer constituted by amaterial containing at least nitrogen on a transparent substrate whichis to be used in an exposing device utilizing such high power exposingmeans as to promote a forming reaction of a foreign matter constitutedby ammonium sulfate, wherein the layer constituted by the materialcontaining at least nitrogen is subjected to surface reforming by anammonium ion formation preventing treatment carried out after formingthe pattern.
 20. The lithographic mask according to claim 19, whereinthe lithographic mask is a photomask to be used in an exposing devicehaving an exposed light in a wavelength of 200 nm or less.
 21. Thelithographic mask according to claim 20, wherein the lithographic maskis a phase shift mask to be used in an exposing device including an ArFexcimer laser as an exposed light source, and the pattern has, on atleast an uppermost layer, a semitranslucent film containing molybdenum,silicon and nitrogen.